Oil additives and compositions

ABSTRACT

PCT No. PCT/EP95/02037 Sec. 371 Date Jan. 10, 1997 Sec. 102(e) Date Jan. 10, 1997 PCT Filed May 26, 1995 PCT Pub. No. WO95/33021 PCT Pub. Date Dec. 7, 1995Oil-soluble polar nitrogen components are used in combination with fuel oil antifoams to control foaming in fuel oils.

This invention relates to oil compositions, primarily to fuel oilcompositions, and more especially to the control of foaming in suchcompositions.

In the processing and transport of liquid fuels, foaming frequentlyoccurs as the fuel is passed from one vessel to another. The foaming mayinterfere with the pumping of the fuel, and may be such as to require areduction in pumping rate to allow foam collapse to avoid fuel spills.It is desirable to control foaming to permit higher rates of fueltransfer. U.S. Pat. No. 3,233,986 describes certain organosiliconcompounds as additives for reducing the foaming tendency of organicliquids such as liquid hydrocarbon fuels. Additives having the abilityto reduce foaming tendency are generally known as "antifoams".

A problem in using antifoams is that relatively large proportionsthereof may be needed to give rise to a desired antifoaming effect.

It has now surprisingly been found that less antifoam is needed toachieve a given antifoaming effect if the antifoam is used incombination with certain other additives such as polar nitrogencompounds. UK-A-1538 578; EP-A-061 894; EP-A-104 015; and EP-A-155 171are examples of specifications describing the use of polar nitrogencompounds as additives in fuel oils, and EP-A-316,108 describes theanti-foaming characteristics of certain substituted amino-sulphosuccinates in diesel fuels.

EP-A-316,108 describes said anti-foam characteristics alone and incombination with an ethylene/propylene copolymer or with anethylene/vinyl acetate copolymer, where the additive componentconcentrations are 116 ppm. It also compares said characteristics withthose of a diesel fuel containing an unspecified conventional siliconeanti-foam.

A first aspect of the invention is a fuel oil composition comprising amajor proportion of a fuel oil and a minor proportion of a combinationof additive components (A) and (B) wherein

(A) comprises a fuel oil antifoam, and

(B) comprises an oil-soluble polar nitrogen compound carrying one ormore, preferably two or more, substituents of the formula --NR¹ --,where R¹ represents a hydrocarbyl group containing 8 to 40 carbon atoms,which substituent or one or more of which substituents may be in theform of a cation derived therefrom.

Component (B) is found to enhance the antifoaming effect of component(A) in both the senses of acceleration of foam collapse and reducedinitial foam height. Thus, the invention enables less of component (A)to be used to achieve a desired antifoam effect.

Second and third aspects of the invention are use of the combination ofadditives (A) and (B) to enhance the antifoaming properties of a fueloil and use of additive (B) to enhance the antifoaming properties ofadditive (A) in a fuel oil, additives (A) and (B) being defined asabove.

The features of the invention will now be described in more detail asfollows:

FUEL OIL

The fuel oil may be a petroleum-based fuel oil, suitably a middledistillate fuel oil, i.e. a fuel oil obtained in refining crude oil asthe fraction between the lighter kerosene and jet fuels fraction and theheavier fuel oil fraction. Such distillate fuel oils generally boilwithin the range of about 100° C. to about 500° C., e.g. 150° to about400° C. (ASTM-D86). The fuel oil can comprise atmospheric distillate orvacuum distillate, or cracked gas oil or a blend in any proportion ofstraight run and thermally and/or catalytically cracked distillates. Themost common petroleum distillate fuels are kerosene, jet fuels, dieselfuels, heating oils and heavy fuel oils. The heating oil may be astraight atmospheric distillate, or it may contain minor amounts, e.g.up to 35 wt %, of vacuum gas oil or cracked gas oils or of both.

Heating oils may be made of a blend of virgin distillate, e.g. gas oil,naphtha, etc. and cracked distillates, e.g. catalytic cycle shock. Arepresentative specification for a diesel fuel includes a minimum flashpoint of 38° C. and a 90% distillation point between 282° and 338° C.(see ASTM Designations D-396 and D-975).

The fuel oil may be an animal, vegetable or mineral oil or a combinationthereof.

COMPONENT (A)

The antifoam is advantageously insoluble in the fuel being treated butis dispersible therein to form a stable dispersion, if necessary withthe aid of a suitable dispersant or solvent, with or without the use ofmechanical dispersing aids.

As antifoam there may be used a siloxane-containing composition. Such acomposition is advantageously a block copolymer containing siloxaneblocks and polyoxyalkylene blocks. The siloxane blocks advantageouslycontain at least two groups of the formula ##STR1## where R represents ahydrocarbyl or hydrocarbylene group, and b has a value within the rangeof from 1 to 4, the ratio of hyrocarbyl or hydrocarbylene groups tosilicon atoms being from 1:1 to 3:1.

The polyoxyalkylene blocks advantageously contain at least twopolyoxyalkylene groups, preferably from 4 to 30 such groups.Advantageously at least 60% by weight of the polyoxyalkylene blocks arerepresented by oxyethylene or oxypropylene units. The block copolymersare advantageously prepared as described in U.S. Pat. No. 3,233,986, thedisclosure of which is incorporated by reference herein.

Examples of such a polyether polymethyl siloxane copolymer compositionsare available commercially. DE-C-4, 343, 235 describes polysiloxaneswith methyl and polar organic substituents that are used to defoamdiesel fuel. Other examples of silicon-containing antifoams are siliconeterpolymers comprising a silicone backbone co-grafted with a phenolderivative (especially eugenol) as well as a polyether, as described inU.S. Pat. No. 5,334,227.

There may alternatively be used an ashless antifoam, for example, acarboxylated polyamine, especially one that is a reaction product of apolyamine of the formula

    NH.sub.2 --R.sup.21 -- --NH--R.sup.22 --!.sub.x -- NH--R.sup.23 !.sub.y --NH.sub.2

with a monocarboxylic acylating agent of the formula

    R.sup.24 COX

wherein, R²¹, R²² and R²³, which may be the same of different, representhydrocarbylene groups and R²⁴ represents a hydrocarbyl group, X is aleaving group, and x and y are integers whose sum is in the range of 0to 10. As used in this specification, the term "ashless" refers to anorganic material that forms substantially no ash on combustion. WO94/06894 describes examples of such ashless antifoams.

As used in this specification the term "hydrocarbyl" refers to a grouphaving a carbon atom directly attached to the rest of the molecule andhaving a hydrocarbon or predominantly hydrocarbon character.

Among these, there may be mentioned hydrocarbon groups, includingaliphatic, (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl orcycloalkenyl), aromatic, aliphatic- and alicyclic-substituted aromatics,and aromatic-substituted aliphatic and alicyclic groups. Aliphaticgroups are advantageously saturated. Examples include methyl, ethyl,propyl, butyl, isobutyl, pentyl, hexyl, octyl, decyl, octadecyl,cyclohexyl, and phenyl. These groups may, as indicated above, containnon-hydrocarbon substituents provided they do not alter thepredominantly hydrocarbon character of the group. Examples include keto,halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl groupis substituted, a single (mono) substituent is preferred. Examples ofsubstituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl,4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl. The groupsmay also or alternatively contain atoms other than carbon in a chain orring otherwise composed of carbon atoms. Suitable hetero atoms include,for example, nitrogen, oxygen and sulfur.

The term "hydrocarbylene" is used analogously. Advantageously such agroup is attached at both valences to the rest of the molecule by carbonatoms.

Advantageously, the polyamine is a polyalkylene polyamine or ahydroxyalkyl polyamine, for example, 1,2-diaminobutan-4-ol.

Advantageously, the acylating agent is a fatty acid, e.g., stearic,oleic or cekanoic acid, or a coco fatty acid fraction. Advantageously,the reaction product is formed by reaction between one mole of polyamineand at least two moles of acylating agent, and preferably the aminegroups of the polyamine are completely acylated.

Examples of suitable products are the reaction product of1,2-diaminobutan-4-ol and a coco-fatty acid fraction, or an N-2-(2-heptadecyl-4,5-dihydro-1H imidazol-1-yl)ethyl! alkamide, e.g.,lauramide.

COMPONENT (B)

The oil-soluble polar nitrogen compound is either ionic or non-ionic andis capable of acting as a wax crystal growth inhibitor in fuels. Itcomprises for example one or more of the compounds (i) to (iii) asfollows:

(i) An amine salt and/or amide formed by reacting at least one molarproportion of a hydrocarbyl substituted amine with a molar proportion ofa hydrocarbyl acid having 1 to 4 carboxylic acid groups or itsanhydride, the substituent(s) of formula --NR¹ --being of the formula--NR¹ R² where R¹ is defined as in the first aspect of the invention andR² represents hydrogen or R¹, provided that R¹ and R² may be the same ofdifferent, said substituents constituting part of the amine salt and/oramide groups of the compound.

Ester/amides may be used containing 30 to 300, preferably 50 to 150total carbon atoms. These nitrogen compounds are described in U.S. Pat.No. 4,211,534. Suitable amines are usually long chain C₁₂ -C₄₀ primary,secondary, tertiary or quaternary amines or mixtures thereof but shorterchain amines may be used provided the resulting nitrogen compound is oilsoluble and therefore normally contains about 30 to 300 total carbonatoms. The nitrogen compound preferably contains at least one straightchain C₈ to C₄₀, preferably C₁₄ to C₂₄, alkyl segment.

Suitable amines include primary, secondary, tertiary or quaternary, butpreferably are secondary. Tertiary and quaternary amines can only formamine salts. Examples of amines include tetradecyl amine, cocoamine, andhydrogenated tallow amine. Examples of secondary amines includedioctacedyl amine and methyl-behenyl amine. Amine mixtures are alsosuitable such as those derived from natural materials. A preferred amineis a secondary hydrogenated tallow amine of the formula HNR¹ R² whereinR¹ and R² are alkyl groups derived from hydrogenated tallow fat composedof approximately 4% C₁₄, 31% C₁₆, 59% C₁₈.

Examples of suitable carboxylic acids and their anhydrides for preparingthe nitrogen compounds include cyclohexane 1,2 dicarboxylic acid,cyclohexene 1,2 dicarboxylic acid, cyclopentane 1,2 dicarboxylic acidand naphthalene dicarboxylic acid, and 1,4-dicarboxylic acids includingdialkyl spirobislactone. Generally, these acids have about 5-13 carbonatoms in the cyclic moiety. Preferred acids useful in the presentinvention are benzene dicarboxylic acids such as phthalic acid,isophthalic acid, and terephthalic acid. Phthalic acid or its anhydrideis particularly preferred. The particularly preferred compound is theamide-amine salt formed by reacting 1 molar portion of phthalicanhydride with 2 molar portions of dihydrogenated tallow amine. Anotherpreferred compound is the diamide formed by dehydrating this amide-aminesalt.

Other examples are long chain alkyl or alkylene substituted dicarboxylicacid derivatives such as amine salts of monoamides of substitutedsuccinic acids, examples of which are known in the art and described inU.S. Pat. No. 4,147,520, for example. Suitable amines may be thosedescribed above.

Other examples are condensates such as described in EP-A-327,423.

(ii) A chemical compound comprising or including a cyclic ring system,the compound carrying at least two substituents of the general formula(1) below on the ring system

    --A--NR.sup.1 R.sup.2                                      (I)

where A is an aliphatic hydrocarbyl group that is optionally interruptedby one or more hetero atoms and that is straight chain or branched, andR¹ is defined as above and R² is independently R¹.

Preferably, A has from 1 to 20 carbon atoms and is preferably amethylene or polymethylene group.

The term "hydrocarbyl" is defined as above.

The cyclic ring system may include homocyclic, heterocyclic, or fusedpolycyclic assemblies, or a system where two or more such cyclicassemblies are joined to one another and in which the cyclic assembliesmay be the same or different. Where there are two or more such cyclicassemblies, the substituents of the general formula (I) may be on thesame or different assemblies, preferably on the same assembly.Preferably, the or each cyclic assembly is aromatic, more preferably abenzene ring. Most preferably, the cyclic ring system is a singlebenzene ring when it is preferred that the substituents are in the orthoor meta positions, which benzene ring may be optionally furthersubstituted.

The ring atoms in the cyclic assembly or assemblies are preferablycarbon atoms but may for example include one or more ring N, S or Oatom, in which case or cases the compound is a heterocyclic compound.

Examples of such polycyclic assemblies include

(a) condensed benzene structures such as naphthalene, anthracene,phenanthrene, and pyrene;

(b) condensed ring structures where none of or not all of the rings arebenzene such as azulene, indene, hydroindene, fluorene, and diphenyleneoxide;

(c) rings joined "end-on" such as diphenyl;

(d) heterocyclic compounds such as quinoline, indole, 2:3 dihydroindole,benzofuran, coumarin, isocoumarin, benzothiophen, carbazole andthiodiphenylamine;

(e) non-aromatic or partially saturated ring systems such as decalin(i.e. decahydronaphthalene), alpha-pinene, cardinene, and bornylene; and

(f) three-dimensional structures such as norbornene, bicycloheptane(i.e. norbornane), bicyclooctane, and bicyclooctene.

Each hydrocarbyl group constituting R¹ and R² (Formula I) may forexample be an alkyl or alkylene group or a mono- or poly-alkoxyalkylgroup. Preferably, each hydrocarbyl group is a straight chain alkylgroup. The number of carbon atoms in each hydrocarbyl group ispreferably 16 to 40, more preferably 16 to 24.

Also, it is preferred that the cyclic system is substituted with onlytwo substituents of the general formula (I) and that A is a methylenegroup.

Examples of salts of the chemical compounds are the acetate and thehydrochloride.

The compounds may conveniently be made by reducing the correspondingamide which may be made by reacting a secondary amine with theappropriate acid chloride. Examples of such compounds are described inWO 9304148 (PCT/EP92101924).

(iii) A condensate of a primary amine of formula R¹ NH₂ or a secondaryamine of formula R¹ R² --NH with a carboxylic acid-containing polymerwhere R¹ is defined as above and R² is independently R¹.

Specific examples include polymers such as described in GB-A-2,121,807,FR-A-2,592,387 and DE-A-3,941,561; and also esters of telemer acid andalkanoloamines such as described in U.S. Pat. No. 4,639,256; and thereaction product of an amine containing a branched carboxylic acidester, an epoxide and a mono-carboxylic acid polyester such as describedin U.S. Pat. No. 4,631,071.

TREAT RATES

The concentration of the additive (B) in the fuel oil may for example bein the range of 1 to 5,000 ppm (active ingredient) by weight per weightof fuel, for example 5 to 5,000 ppm such as 5 to 2000 ppm (activeingredient) by weight per weight of fuel, preferably 5 to 500 ppm morepreferably 5 to 200 ppm.

The concentration of additive (A) (antifoam) in the fuel oil may, forexample, be in the range of 0.5 to 5,000 ppm (active ingredient) byweight per weight of fuel such as 0.5 to 200 ppm, preferably 0.5 to 25ppm, more preferably 0.5 to 15 ppm, such as 0.5 to 5 ppm (e.g. 1, 2, 3,or 4 ppm).

Component (B) is known as a flow improver additive in fuel oils and itis found in this invention that, when used at treat rates where it isactive as a flow improver additive (e.g. above 200 ppm), it enhances theantifoam properties of component (A). It is further found in thisinvention that, when component (B) is used at treat rates below those atwhich it is active as a flow improver additive, (e.g. less than 200 ppm,such as 1-50, preferably 1-15 such as 4-12, more preferably 1-10 ppm),it still enhances the antifoam properties of component (A).

A benefit of the invention is thus that the invention is applicable whencold flow properties are not required, e.g. in the summer, by using alow treat rate of component (B), and also when cold flow properties arerequired, e.g. in the winter, by using a high treat rate of component(B).

A further benefit of the present invention is that components (A) and(B) can be added in combination to the fuel oil, thereby optimising andcontrolling their combined anti-foam effect in relation to treat rate.If they are added separately, it may not be possible to take account oftheir synergy and more of a component than is necessary may be added.

CO-ADDITIVES

The additives of the invention may be used singly or as mixtures. Theymay also be used in combination with one or more other co-additives suchas known in the art, for example the following: detergents,antioxidants, corrosion inhibitors, dehazers, demulsifiers, metaldeactivators, cetane improvers, cosolvents, package compatibilisers, andlubricity additives. Also, other flow improvers may be used asco-additives, examples including ethylene/unsaturated ester copolymers,and comb polymers which are discussed below.

Ethylene copolymer flow improvers, i.e. ethylene unsaturated estercopolymer flow improvers, have a polymethylene backbone divided intosegments by oxyhydrocarbon side chains.

More especially, the copolymer may comprise an ethylene copolymerhaving, in addition to units derived from ethylene, units of the formula

    --CR.sup.5 R.sup.6 --CHR.sup.7 --

wherein R⁶ represents hydrogen or a methyl group;

R⁵ represents a --OOCR⁸ or --COOR⁸ group wherein R⁸ represents hydrogenor a C₁ to C₂₈, preferably C₁ to C₉, straight or branched chain alkylgroup, provided that R⁸ does not represent hydrogen when R⁵ represents--COOR⁸ ; and R⁷ is hydrogen or --COOR⁸.

These may comprise a copolymer of ethylene with an ethylenicallyunsaturated ester, or derivatives thereof. An example is a copolymer ofethylene with an ester of an unsaturated carboxylic acid, but the esteris preferably one of an unsaturated alcohol with a saturated carboxylicacid. An ethylene-vinyl ester copolymer is advantageous; anethylene-vinyl acetate, ethylene vinyl propionate, ethylene-vinylhexanoate, or ethylene-vinyl octanoate copolymer is preferred.Preferably, the copolymers contain from 1 to 25, e.g. 1 to 20, mole % ofthe vinyl ester, more preferably from 3 to 15 mole % vinyl ester. Theymay also be in the form of mixtures of two copolymers such as thosedescribed in U.S. Pat. No. 3,961,916. Preferably, number averagemolecular weight, as measured by vapour phase osmometry, of thecopolymer is 1,000 to 10,000, more preferably 1,000 to 5,000. Ifdesired, the copolymers may be derived from additional comonomers, e.g.they may be terpolymers or tetrapolymers or higher polymers, for examplewhere the additional comonomer is isobutylene or diisobutylene.

The copolymers may be made by direct polymerisation of comonomers. Suchcopolymers may also be made by transesterification, or by hydrolysis andre-esterification, of an ethylene unsaturated ester copolymer to give adifferent ethylene unsaturated ester copolymer. For example, ethylenevinyl hexanoate and ethylene vinyl octanoate copolymers may be made inthis way, e.g. from an ethylene vinyl acetate copolymer.

Comb polymers are discussed in "Comb-Like Polymers. Structure andProperties", N. A. Plate and V. P. Shibaev, J. Poly. Sci. MacromolecularRevs., 8, p 117 to 253 (1974).

Generally, comb polymers have one or more long chain branches such ashydrocarbyl branches, such as oxyhydrocarbyl branches, having from 10 to30 carbon atoms, pendant from a polymer backbone, said branch orbranches being bonded directly or indirectly to the backbone. Examplesof indirect bonding include bonding via interposed atoms or groups,which bonding can include covalent and/or electrovalent bonding such asin a salt.

Advantageously, the comb polymer is a homopolymer having, or a copolymerat least 25 and preferably at least 40, more preferably at least 50,molar per cent of the unts of which have, side chains containing atleast 6, and preferably at least 10, atoms, selected from for examplecarbon, nitrogen and oxygen, in a linear chain.

As examples of preferred comb polymers there may be mentioned thosecontaining units of the general formula ##STR2## where D=R¹¹, COOR¹¹,OCOR¹¹, R¹² COOR¹¹ or OR¹¹

E=H, CH₃, D or R¹²

G=H or D

J=H, R¹², R¹² COOR¹¹, or an aryl or heterocyclic group

K=H, COOR¹², OCOR¹², OR¹² or COOH

L=H, R¹², COOR¹², OCOR¹² or aryl

R¹¹ ≧C₁₀ hydrocarbyl

R¹² ≧C₁ hydrocarbyl

and m and n represent mole ratios, their sum being 1 and m being finiteand being up to and including 1 and n being from zero to less than 1,preferably m being within the range of from 1.0 to 0.4, n being in therange of from 0 to 0.6. R¹¹ advantageously represents a hydrocarbylgroup with from 10 to 30 carbon atoms, and R¹² advantageously representsa hydrocarbyl group with from 1 to 30 carbon atoms.

The comb polymer may contain units derived from other monomers ifdesired or required. It is within the scope of the invention to includetwo or more different comb copolymers.

These comb polymers may be copolymers of maleic anhydride or fumaricacid and another ethylenically unsaturated monomer, e.g. an a-olefin oran unsaturated ester, for example, vinyl acetate. It is preferred butnot essential that equimolar amounts of the comonomers be used althoughmolar proportions in the range of 2 to 1 and 1 to 2 are suitable.Examples of olefins that may be copolymerized with e.g. maleicanhydride, include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene,and 1-octadecene.

The copolymer may be esterified by any suitable technique and althoughpreferred it is not essential that the maleic anhydride or fumaric acidbe at least 50% esterified. Examples of alcohols which may be usedinclude n-decan-1-ol, n-dodecan-1-ol, n-tetradecan-1-ol,n-hexadecan-1-ol, and n-octadecan-1-ol. The alcohols may also include upto one methyl branch per chain, for example, 1-methylpentadecan-1-ol,2-methyltridecan-1-ol. The alcohol may be a mixture of normal and singlemethyl branched alcohols. It is preferred to use pure alcohols ratherthan the commercially available alcohol mixtures but if mixtures areused the R¹² refers to the average number of carbon atoms in the alkylgroup; if alcohols that contain a branch at the 1 or 2 positions areused R¹² refers to the straight chain backbone segment of the alcohol.

These comb polymers may especially be fumarate or itaconate polymers andcopolymers such as for example those described in European PatentApplications 153 176, 153 177 and 225 688, and WO 91/16407.

Particularly preferred fumarate comb polymers are copolymers of alkylfumarates and vinyl acetate, in which the alkyl groups have from 12 to20 carbon atoms, more especially polymers in which the alkyl groups have14 carbon atoms or in which the alkyl groups are a mixture of C₁₄ /C₁₆alkyl groups, made, for example, by solution copolymerizing an equimolarmixture of fumaric acid and vinyl acetate and reacting the resultingcopolymer with the alcohol or mixture of alcohols, which are preferablystraight chain alcohols. When the mixture is used it is advantageously a1:1 by weight mixture of normal C₁₄ and C₁₆ alcohols. Furthermore,mixtures of the C₁₄ ester with the mixed C₁₄ /C₁₆ ester mayadvantageously be used. In such mixtures, the ratio of C₁₄ to C₁₄ /C₁₆is advantageously in the range of from 1:1 to 4:1, preferably 2:1 to7:2, and most preferably about 3:1, by weight. The particularlypreferred fumarate comb polymers may, for example, have a number averagemolecular weight in the range of 1,000 to 100,000, preferably 1,000 to30,000, as measured by Vapour Phase Osmometry (VPO).

Other suitable comb polymers are the polymers and copolymers ofalpha-olefins and esterified copolymers of styrene and maleic anhydride,and esterified copolymers of styrene and fumaric acid; mixtures of twoor more comb polymers may be used in accordance with the invention and,as indicated above, such use may be advantageous.

Other examples of comb polymers are hydrocarbon polymers such ascopolymers of ethylene and at least one α-olefin, preferably theα-olefin having at most 20 carbon atoms, examples being n-decene-1 andn-dodecene-1. Preferably, the number average molecular weight of such acopolymer is at least 30,000. The hydrocarbon copolymers may be preparedby methods known in the art, for example using a Ziegler type catalyst.

Examples of other flow improver additives include hydrocarbon polymers(e.g. ethylene--lower alpha olefin e.g. propylene! copolymers), andcompounds such as described in EP-A-61895, JP 2-51477 and 3-34790,EP-A-117,108, EP-A-326,356 and EP-A-356,256.

Mono- or poly-carboxylic acids such as benzoic acid may be included asstabilisers.

CONCENTRATES

Concentrates are convenient as a means for incorporating the additivesinto bulk fuel oil, which incorporation may be done by methods known inthe art. The concentrates may also contain other additives as requiredand preferably contain from 3 to 75 wt %, more preferably 3 to 60 wt %,most preferably 10 to 50 wt % of the additives preferably in solution inoil. Examples of carrier liquid are organic solvents includinghydrocarbon solvents, for example petroleum fractions such as naphtha,kerosene, diesel and heater oil; aromatic hydrocarbons such as aromaticfractions, e.g. those sold under the `SOLVESSO` tradename; andparaffinic hydrocarbons such as hexane and pentane and isoparaffins. Thecarrier liquid must, of course, be selected having regard to itscompatibility with the additives and with the fuel.

The additives of the invention may be incorporated into the fuel oil byother methods such as those known in the art. If co-additives arerequired, they may be incorporated into the bulk oil at the same time asthe additives of the invention or at a different time.

EXAMPLES

The following examples illustrate the invention, in which the followingmaterials were used and the following test was carried out.

Fuels

Fuels A and B, characterised as follows, were used

    ______________________________________                                                       A     B                                                        ______________________________________                                        Specific Density 0.8398  0.833                                                Cloud Point (°C.)                                                                       -6      -9                                                   ______________________________________                                    

Distillation Characteristics (°C.)

    ______________________________________                                        IBP             163.0                                                         10%                    201                                                    20%             233                                                           50%             277    250                                                    90%             333    321                                                    95%             347                                                           FBP             367    357                                                    ______________________________________                                    

Additives

Antifoam: a polyoxyalkylene modified dimethyl poly-siloxane.

Polar N Compound: a N,N-dialkylammonium salt of 2 --N¹,N¹-dialkylamidobenzoate, being the reaction product of reacting one moleof phthalic anhydride with two moles of dihydrogenated tallow amine toform a half amide/half amine salt.

Test

Samples of the fuels were treated with various additive combinationsand, in each test, agitated vigorously and the time, in seconds, for thefoam to collapse observed. The initial foam height was also measured andthe untreated and treated fuels compared. The examples were carried outat ambient temperature. Additive treat rates are indicated in theexamples below in parts per million (ppm) by weight.

Example 1

Results obtained in Fuel A were as follows:

    ______________________________________                                                         Collapse Time                                                                            Foam Height                                       Additive (treat rate, ppm)                                                                     (sec)      Reduction (%)                                     ______________________________________                                        Untreated        26          0                                                Antifoam (12.5)  12         26                                                Polar N Compound (200)                                                                         23          6                                                Antifoam (12.5) + Polar N                                                                       5         70                                                Compound (200)                                                                ______________________________________                                    

Thus, the polar N compound enhances the antifoam properties of theanti-foam.

Example 2

Results obtained in Fuel B were as follows:

    ______________________________________                                                         Collapse Time                                                                            Foam Height                                       Additive (treat rate, ppm)                                                                     (sec)      Reduction (%)                                     ______________________________________                                        Untreated        23          0                                                Antifoam (12.5)   9         60                                                Polar N Compound (200)                                                                         21          5                                                Antifoam (12.5) + Polar N                                                                       3         70                                                Compound (200)                                                                ______________________________________                                    

Again, the polar N compound enhances the antifoam properties of theantifoam.

Example 3

Further results obtained in Fuel A were as follows:

    ______________________________________                                                         Collapse Time                                                                            Foam Height                                       Additive (treat rate, ppm)                                                                     (sec)      Reduction (%)                                     ______________________________________                                        Untreated        30         0                                                 Antifoam (10)    10         43                                                Antifoam (2) + Polar N                                                                         10         43                                                Compound (224)                                                                Antifoam (2) + Polar N                                                                         9          43                                                Compound (224) + nonyl                                                        phenol (50                                                                    Antifoam (2) + Polar N                                                                         8          43                                                Compound (224) + benzoic                                                      acid (50)                                                                     ______________________________________                                    

Thus, use of the polar N compound enable 8 ppm less of antifoam to beused to obtain the same anti-foam properties. Antifoam performance wasfurther enhanced by additions of nonyl phenol and of benzoic acid.

The additives also contained a fumarate comb polymer co-additive, otherco-additives known in the art and solvents.

Example 4

Further results obtained in a diesel fuel of the followingcharacteristics were as follows:

    ______________________________________                                        Specific Density (15° C.)                                              Distillation Characteristics (°C.)                                                         0.8365                                                    ______________________________________                                        IBP                 195                                                       10%                 222                                                       20%                 233                                                       50%                 264                                                       90%                 331                                                       95%                 351                                                       FBP                 370                                                       ______________________________________                                                     1   2       4     8     15  22                                   Additive (treat rate, ppm)                                                                   (Days)                                                         ______________________________________                                        Untreated      39    45          41    44  45                                 Antifoam (4)   4     8       11  13    22                                     Antifoam (8)         8       10  13    14                                     Antifoam (12)  0     2           5     8   13                                 Antifoam (8) + 0     4           6     9   15                                 Polar N Compound (4)                                                          Antifoam (8) + 0     4           6     11  22                                 Polar N Compound (12)                                                         ______________________________________                                    

The above results indicate foam collapse time in seconds after anindicated number of days and show that very low treat rates of the PolarN Compound were effective in enhancing the antifoam performance of theAntifoam and that such enhancement is retained over a period of time.

We claim:
 1. A fuel oil composition comprising a major proportion of amiddle distillate fuel oil and a minor proportion of both additives (A)and (B) whereinadditive (A) comprises from about 0.5 to about 5000 ppmby weight active ingredient of a fuel oil antifoam which is asiloxane-containing composition, and additive (B) comprises from about 1to about 5000 ppm by weight active ingredient of an oil-soluble polarnitrogen compound carrying one or more substituents of the formula --NR¹-- or a cation salt thereof, where R¹ represents a hydrocarbyl groupcontaining 8 to 40 carbon atoms.
 2. A fuel oil composition of claim 1wherein the siloxane-containing composition is a block copolymercontaining siloxane blocks and polyoxylalkylene blocks.
 3. A fuel oilcomposition of claim 1 wherein the oil-soluble polar nitrogen compoundis an amine salt and/or amide formed by reacting at least one molarproportion of a hydrocarbyl substituted amine with a molar proportion ofa hydrocarbyl acid having 1 to 4 carboxylic acid groups or itsanhydride, the substituent(s) of formula --NR¹ -- being of theformula--NR¹ R² where R¹ is defined as in claim 1 and R² representshydrogen or R¹, provided that R¹ and R² may be the same or different,said substituents constituting part of the amine salt and/or amidegroups of the compound.
 4. A fuel oil composition of claim 3 wherein atleast one of R¹ and R² represent a straight chain alkyl group havingfrom 14 to 24 carbon atoms.
 5. A fuel oil composition of claim 1 whereinthe oil-soluble polar nitrogen compound comprises or includes a cyclicring system carrying at least two substituents of the formula --A--NR¹R² wherein A is an aliphatic hydrocarbyl group that is optionallyinterrupted by one or more hetero atoms and that is straight chain orbranched, and R¹ is defined as in claim 1 and R² is independently R¹. 6.A fuel oil composition of claim 1 wherein the oil-soluble polar nitrogencompound is a condensate of a primary amine of formula R¹ NH₂ or asecondary amine of formula R¹ R² NH with a carboxylic acid-containingpolymer wherein R¹ is defined as in claim 1 and R² is independently R¹.7. A fuel oil composition of claim 1 which comprises 0.5 to 15 ppm byweight of additive (A) antifoam per weight of fuel oil.
 8. A fuel oilcomposition of claim 7 which comprises 0.5 to 5 ppm by weight ofadditive (A) antifoam per weight of fuel oil.
 9. A fuel oil compositionof claim 1 wherein the fuel oil is a diesel fuel.
 10. A fuel oilcomposition of claim 7 which comprises 1 to 50 ppm by weight of additive(B) per weight of fuel oil.
 11. A fuel oil composition of claim 10wherein there is 1 to 15 ppm of additive (B).
 12. A fuel oil compositionof claim 2 wherein the block polymer containing siloxane blocks andpolyoxyalkylene blocks is a polyoxyalkylene modified dimethylpolysiloxane.
 13. A fuel oil composition of claim 12 wherein the oilsoluble polar nitrogen compound of additive (B) is a N,N-dialkylammoniumsalt of 2-N',N'-dialkylamidobenzoate, being the reaction product ofreacting one mole of phthalic anhydride with two moles of dehydrogenatedtallow amine to form a half amide/half amine salt.
 14. A method ofenhancing the acceleration of foam collapse and reduced initial foamheight properties of middle distillate fuel oil obtained from anantifoam which is a siloxane containing composition, which methodcomprises adding to the fuel oil a minor proportion of both additives(A) and (B) whereinadditive (A) comprises from about 0.5 to about 5000ppm by weight active ingredient of a fuel oil antifoam which is asiloxane-containing composition, and additive (B) comprises from about 1to about 5000 ppm by weight active ingredient of an oil-soluble polarnitrogen compound carrying one or more substituents of the formula --NR¹-- or a cation salt thereof, where R¹ represents a hydrocarbyl groupcontaining 8 to 40 carbon atoms.
 15. A method of claim 14 wherein thesiloxane-containing composition is a block copolymer containing siloxaneblocks and polyoxylalkylene blocks and the oil-soluble polar nitrogencompound is an amine salt and/or amide formed by reacting at least onemolar proportion of a hydrocarbyl substituted amine with a molarproportion of a hydrocarbyl acid having 1 to 4 carboxylic acid groups orits anhydride, the substituent(s) of formula --NR¹ -- being of theformula --NR¹ R² where R¹ is defined as in claim 1 and R² representshydrogen or R¹, provided that R¹ and R² may be the same or different,said substituents constituting part of the amine salt and/or amidegroups of the compound.
 16. A method of claim 15 wherein the blockcopolymer containing siloxane blocks and polyoxyalkylene blocks is apolyoxyalkylene modified dimethyl polysiloxane.
 17. A method of claim 16wherein the oil soluble polar nitrogen compound of additive (B) is aN,N-dialkylammonium salt of 2-N',N'-dialkylamidobenzoate, being thereaction product of reacting one mole of phthalic anhydride with twomoles of dehydrogenated tallow amine to form a half amide/half aminesalt.
 18. A fuel oil composition comprising a major proportion of amiddle distillate fuel oil and a minor proportion of additives (A) and(B) whereinadditive (A) comprises from about 0.5 to about 15 ppm byweight active ingredient of an antifoam which is a polyoxyalkylenemodified dimethyl polysiloxane, and additive (B) comprises from about 5to about 500 ppm by weight active ingredient of an oil soluble polarN,N-dialkylammonium salt of 2-N'N'-dialkylamidobenzoate, being thereaction product of reacting one mole of phthalic anhydride with twomoles of dehydrogenated tallow amine to form a half amide/half aminesalt.